Science Modules for Grade 7
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Transcript of Science Modules for Grade 7
SOLUTIONS
Overview
In Grade 6, you have learned about different mixtures and their
characteristics. You have done activities where you mixed a solid and a liquid or combined two different liquids. In the process of mixing, you have
observed that these mixtures either form homogeneous or heterogeneous mixtures. You have seen that when all parts of the mixture have the same uniform appearance and properties, it is homogeneous.
You also learned that when different parts of the mixture can be identified, it is heterogeneous. An example of a heterogeneous mixture is ice
cubes (solid phase) placed in a glass of soft drink (liquid phase). Different phases can be identified. When all the ice cubes are melted, only one liquid
phase is seen. It is now homogeneous.
Homogeneous mixtures are called solutions. When you put sugar into
water, the solid becomes part of the liquid and cannot be seen. You can say that the sugar dissolves in water or the sugar is soluble in water. Solutions
may be solids dissolved in liquids or gases dissolved in liquids. There are also solutions where a gas is dissolved in another gas, a liquid in another liquid or a solid in another solid. Solutions of gases, liquids, and solids are
all around you. Many commercial products are sold as solutions.
In this module, you will identify common properties of solutions using
different methods. You will also learn how to report the amount of the
components in a given volume of solution. Towards the end of the module,
you will investigate the factors that affect how fast a solid dissolves in water.
What common properties do solutions have?
Are solutions always liquid?
Will all solids dissolve in water?
How fast do solids dissolve in water?
Suggested time allotment: 5 to 6 hours
MODULE
1
Grade 7 Science: Matter 2
Diversity of Materials in the Environment
Activity 1
What Solutions Do You Find In Your Home?
Objectives
After performing this activity, you should be able to:
1. describe the observable characteristics or properties of common
solutions found at home or in the sari-sari store or grocery; and
2. present the data gathered in table form to show the different
properties of common solutions.
You may make a table similar to the one below.
Solution Characteristics
You noticed that you did not see solid particles or liquid droplets in the
samples of solutions. Most of the solutions, which are in liquid phase,
appear clear but some of them are colored.
The solutions that you have observed actually consist of two components
called the solvent and the solute. Generally, the solid or liquid particles
dissolving in solution are called the solute. It is the component present in
small amount. The solvent is the part of the solution that dissolves the
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solute. Usually the solvent is the component present in greater amount. So
in a sugar solution, sugar is the solute and water is the solvent.
You observed in Activity 1 that a solution is not always a liquid; it can be
solid, liquid, or gas. In addition, solutions may either be found in nature or
man-made.
Naturally Occurring Solutions
There are solutions that occur naturally.These are natural bodies of
water like the seas and ocean, blood plasma, digested food, air, and mineral
ores.
Many materials in nature can be used efficiently only when these are
in the form of solutions. For example, plants cannot absorb minerals from
the soil unless these minerals are in solution. The food that you eat is
changed into solution during digestion. The nutrient particles in solution
can pass through the digestive tract and dissolve in the blood.
Seawater is a solution having a higher percentage of salt and minerals
than any other natural source of water. Similarly, rainwater is a solution
containing dissolved gases like oxygen, carbon dioxide, and other gases.
The water you drink contains dissolved minerals ions, like sodium,
potassium, magnesium and calcium and dissolved gases like oxygen and
carbon dioxide.
Blood plasma is a good example of a solution present in our body. It is
a clear, transparent, pale yellow fluid with a uniform composition
throughout.
Air is a mixture of gases. Any sample of dry air consists of about 78%
nitrogen, 21% oxygen, 1% argon, about 1% water vapor, and 0.04% carbon
dioxide. Air also contains traces of ozone, hydrogen, helium, neon, krypton,
and xenon. Water vapor is present in different amounts depending on the
location. Air above big bodies of water contains more water vapor than air
above deserts.
Useful solutions are not only found in nature, many solutions are
made for a specific purpose.
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Diversity of Materials in the Environment
Manufactured/Processed Solutions
Almost every household uses vinegar for cooking and cleaning
purposes. Vinegar is a homogeneous mixture usually contains about 5%
acetic acid in water.
Gasoline is a solution made up mostly of liquids at room temperature.
It is important that gasoline is in one phase only because any solid particles
in it will clog the fuel filter of the vehicle.
A metal alloy is a solid solution made up of two or more metals or non
metals. For example, steel is an alloy of copper and tin. Brass is an alloy of
copper and zinc.
Other examples of solutions that are processed include wine and
liquor, juices made from powdered fruit flavors, brewed coffee and tea.
In the next activity, you will predict what will happen when you mix a
sample solid or liquid in a given volume of water. Investigate to find out if
your predictions are correct. Explain your predictions using the evidence
you have gathered from your investigation.
Activity 2
What are the properties of solutions?
When you finish this activity you should be able to:
1. compare the evidence gathered with the predictions you made;
2. identify the solute and the solvent in a solution; and
3. describe two ways of identifying a solution.
Materials Needed:
6 cups water
6 pieces, spoons
cheesecloth (katsa) or filter paper
2 tablespoons each of the following: sugar, salt, mongo seeds,
powdered juice, cooking oil, vinegar
12 clear bottles or cups
2 pieces each, measuring spoons (½ tsp and 1tsp)
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2 pieces each, measuring cups (½ cup and 1cup)
3 funnels
3 funnel racks
Procedure:
1. Given the materials listed in Table 1, column 1:
a. Predict which among the given solids will dissolve in water.
My prediction: ____________________________________________
b. Predict which among the given liquids will mix well with water.
My prediction: _____________________________________________
2. Mix ½ teaspoon of the sample solid or liquid with ½ cup water. Use the
teaspoon to dissolve as much of each sample as possible. Use a different
teaspoon for each of the cups.
Q1. Did the solid or liquid dissolve in water?
Q2. Which of the samples dissolved completely? What is your evidence?
Q3. Which of the samples dissolved partially (not completely)?
Q4. Which samples seemed not to dissolve at all? Q5. What is the appearance of the mixture?
Q6. Identify the solute and the solvent in each of the mixtures.
Write your answers to Q1 to Q5 in columns 2 and 3 of Table 1.
Table 1. Data table for Activity 2 (1)
Sample solid or liquid
(2) Dissolved in/mixed
well with water (completely,
partially or not at all)
(3) Appearance (uniform or not uniform)
(4) Can be
separated by filtration
(yes or no)
(5) Taste of filtrate
Sugar
Salt
Mongo seeds
Powdered
juice
Cooking oil
Vinegar
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Never taste any sample unless asked by the teacher or written in the activity procedure.
3. Filter the solution with cheesecloth or filter paper using a setup similar
to Figure 1.
* Philippines. Department of Education. (2004). Chemistry: Science and Technology
textbook for 3rd year. (Revised ed.). Quezon City: Author.
Q7. In which mixture were you able to separate the components (solute and
solvent) by filtration? Write your observations in column 4 of Table 1.
4. Since all the samples are food items, get a small amount of the sample
using a clean teaspoon and taste the filtrate (the liquid that passes
through the filter). Wash and clean each teaspoon you will use for
tasting.
Q8. What was the taste of each of the filtrate?
Q9. Using all the data you collected, what are the properties of solutions?
Figure 1. A filtration setup. The funnel is supported on an iron ring and the filtrate is received in
another container.*
TAKE CARE!
Grade 7 Science: Matter 7
Diversity of Materials in the Environment
In Activity 2, you found out that a solution is formed when a solute
dissolves in a solvent to form a single phase that appears uniform
throughout. A solution is clear but it can be either colored or colorless. In a
solution, the particles are too small that they cannot be seen by the unaided
eye. The particles in solution are smaller than the pores of the filter paper or
the cheesecloth and so these can pass through the filter.
Each part of a solution retains its characteristic properties. When you
filtered the sugar solution, the filtrate still tasted sweet. The sweetness of
sugar is present in any part of the sugar solution.
Based on the results of Activity 2, there are common properties that
solutions have.
There are other ways of identifying a solution. You will learn these
methods in Grades 8 and 9.
In Activity 3, you will find out how much solute can dissolve in a given
amount of solvent and find out the type of solution based on whether there
is excess solute or not.
At higher grade levels, you will learn more of the detailed processes
that happen when a solute dissolves in a solvent.
Based on the two activities you have done, can you conclude that
solutions have the following characteristics?
1. It is homogeneous. It is a mixture of one phase only. The
components are so well mixed that all parts of the solution
appear the same. Solutions have the same composition and
properties throughout.
2. The solute cannot be separated from the solvent through
filtration because these are so small that they pass through the
filter paper or cheesecloth.
3. A solution is often clear and transparent, whether it is colored
or colorless.
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Diversity of Materials in the Environment
Activity 3
Can You Tell the Difference Between Solutions by the
Way They Look?
After performing this activity you will be able to:
1. determine if different amounts of solid solute dissolve equally well in
the same volume or amount of water; and
2. find out patterns observed from a data table.
Materials Needed
7 teaspoons sugar
7 teaspoons powdered juice (any flavor)
10 cups of water
3 measuring cups (1cup capacity)
3 measuring cups (½ cup capacity)
3 measuring spoons for each of the following: ½ tsp, 1 tsp
Procedures
1. Label four transparent bottles or beakers to identify the sample and its
amount. For example, ½ teaspoon sugar, 1 teaspoon sugar, 2 teaspoons
sugar, and 3 teaspoons sugar.
2. Mix ½ teaspoon of sugar with ½ cup water in a transparent bottle or
beaker. Use the teaspoon to dissolve as much of the sample as possible.
Record in Table 2 if it dissolves completely, partially, or not at all.
3. Repeat step B using 1, 2, and 3 teaspoons of sugar.
4. Clean the bottles or beakers and label each of the containers with ½
teaspoon salt, 1 teaspoon salt, 2 teaspoons salt, and 3 teaspoons salt.
5. Using a different teaspoon, mix ½ teaspoon of salt with ½ cup water in a
transparent bottle or beaker. Use the teaspoon to dissolve as much of the
sample as possible. Record in Table 2 if it dissolves completely, partially,
or not at all.
6. Repeat step E using 1, 2, and 3 teaspoons of salt.
Grade 7 Science: Matter 9
Diversity of Materials in the Environment
7. Repeat steps D, E and F using powdered juice.
Table 2. Data table for Activity 3
Sample
Dissolves in ½ cup of water
(completely, partially or not at all)
½
teaspoon
1 teaspoon 2 teaspoons 3 teaspoons
Sugar
Salt
Powdered
juice
Q1. How much sugar dissolves completely in ½ cup of water?
Q2. How much salt dissolves completely in ½ cup of water? Q3. How much powdered juice dissolves completely in ½ cup of water?
Q4. Based on your answers to questions (1) to (3), which among the three
samples is the most soluble (the one with the greatest amount of solid that dissolves completely) in ½ cup of water?
In this activity, you have observed that there is a maximum amount of
solute that can dissolve in a given amount of solvent at a certain
temperature. This is what is called the solubility of the solute.
From your everyday experience, you observe that there is a limit to the
amount of sugar you can dissolve in a given amount of water. Solubility
changes with temperature. Your solutions in Activity 3 were at room
temperature. The solubility of these solutions will change if you either
increase or decrease the temperature.
1. In which container(s) did you observe excess solid which did not
dissolve?
The solution that contains the maximum amount of solute dissolved by a
given amount of solvent is called a saturated solution. If you add more
solute to the solvent, it will no longer dissolve. The solution has reached its
saturation point. The presence of an excess solid which can no longer
dissolve is an evidence that the solution is saturated.
Grade 7 Science: Matter 10
Diversity of Materials in the Environment
2. Is there any container where all solids dissolved? Which container is
this?
A solution is unsaturated when it contains less solute than the
maximum amount it can dissolve at a given temperature. In Activity 3, it is
difficult to conclude that the containers with all solids dissolved are
unsaturated simply by observing them. Some of these may already hold the
maximum amount of solute, which cannot be observed by the unaided eye.
So, these are classified as saturated solutions.
A more measurable way to find out the solubility of a solute is to
determine the maximum amount that can be dissolved in 100 g of solvent at
a specific temperature. There are available data from chemistry books that
give the solubility of common solutes at particular temperatures. Figure 2
shows the solubility of table salt at 25oC.
Figure 2. At 25oC, a saturated solution of table salt has only
36.0 g dissolved in 100 mL of water. Any additional table salt will no longer dissolve.
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Concentration of Solutions
The concentration describes the relative amounts of solute and solvent
in a given volume of solution. When there is a large amount of dissolved
solute for a certain volume of solvent, the solution is concentrated. A dilute
solution has a small amount of dissolved solute in comparison to the
amount of solvent.
You will be able to distinguish between concentrated and dilute
solutions from a simple demonstration your teacher will perform. You will
describe the concentrations of solutions qualitatively (by simply observing
their appearance) and quantitatively (by comparing the number of drops per
volume of water).
From Part 1 of the demonstration, you were able to describe the
solutions as having quantitative concentrations of 1 drop/50 mL and 10
drops/50 mL. Qualitatively, you were able to distinguish the bottle with 10
drops/50 mL more concentrated (darker) than the bottle with 1 drop/50 mL.
Now that you have distinguished dilute from concentrated solutions
qualitatively and quantitatively from your teacher’s demonstration, you can
express concentration in other ways such as:
(1) percent by volume, which is the amount of solute in a given
volume of solution expressed as grams solute per 100 millliter of
solution (g/100 mL), and
(2) percent by mass, which is the amount of solute in a given mass of
solvent expressed as grams solute per 100 grams of solution.
Labels of products sold often show the concentrations of solutes
expressed as percent (%) by volume or mass. The alcohol used as a
disinfectant is a solution of 70% ethyl or isopropyl alcohol and 30% water.
There are also solutions sold as 40% ethyl or isopropyl alcohol and 60%
water.
Vinegar is often labeled as “5% acidity,” which means that it contains 5
grams of acetic acid in 100 g of vinegar. The common antiseptic, agua
oxinada is a 3%solution of hydrogen peroxide in water.
The concentration of solid solutions, like gold jewelry, is expressed as
karat. An 18 karat (18K) gold contains 18 parts gold and 6 parts of
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Diversity of Materials in the Environment
another metal, making it 75% gold while a 14 karat (14K) gold contains 14
parts gold and 10 parts of another metal, making it 58.3% gold.
The following sample problems show you that there is a way to know the
exact ratio of solute to solvent, which specifies the concentration of a
solution.
Sample problem 1
How many mL of ethyl alcohol are present in a 50 mL bottle of rubbing
alcohol?
Calculation for sample problem 1
Since rubbing alcohol contains 70% ethyl alcohol, it means that 100
mL of rubbing alcohol contains 70 mL ethyl alcohol and 30 mL water. So,
the following calculations show that in 50 mL of rubbing alcohol, there is 35
mL ethyl alcohol and 15 mL water.
All portions of a solution have the same concentration. The
composition of one part is also the same as the composition of the other
parts. But you can change the concentration of solutions. This means you
can prepare different solutions of sugar in water of different concentrations
(for example, 10%, 20%, or 30%). In the same way, you can prepare different
solutions of salt in water.
Sample problem 2
A one peso coin has a mass of 6.0 grams. How many grams of copper
are in a one peso coin containing 75% copper by mass?
Calculation for sample problem 2
75% by mass means 75 grams of copper in 100 grams of one peso
coin.
50 mL rubbing alcohol x 70 mL ethyl alcohol
100 mL rubbing alcohol = 35 mL ethyl alcohol
Grade 7 Science: Matter 13
Diversity of Materials in the Environment
So, a 6.0 grams coin contains,
75 g copper
100 g coin x 6 g coin = 4.5 g copper
In activities 4 to 6, you will investigate some factors that affect the
amount of solid solute that can dissolve in a given volume of water.
Factors Affecting the Solubility of a Solid Solute
The Effect of Stirring
Your teacher demonstrated the effect of stirring in mixing a solid in
water. You observed that stirring makes the solid dissolve faster in the
solvent. Were you able to explain why this is so?
The Effect of Particle Size
In Activity 4, you will investigate how the size of the solid being
dissolved affects how fast it dissolves in water.
Activity 4
Size Matters!
1. Write a hypothesis in a testable form. Describe a test you could conduct
to find out which dissolves faster: crystals of table salt or the same
amount of crushed salt.
2. Identify variables (for example, amount of table salt) that you need to
control in order to have a fair test.
3. Identify the dependent and independent variables.
4. List all the materials you need, including the amount and ask these from
your teacher.
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Diversity of Materials in the Environment
5. Be sure to record your observations and tabulate them. Write everything
you observed during the dissolving test.
6. What is your conclusion? Does the size of the solid being dissolved affect
the how fast it mixes with water?
7. Does your conclusion support or reject your hypothesis?
8. Based on what you know about dissolving, try to explain your results.
To help you explain the process of dissolving, imagine that in a solution,
the particles of the solute (table salt) and the solvent (water) are constantly
moving. Water particles collide everywhere along the surface of the particles
of table salt, especially on the corners and edges. Why do you think so?
Can you now explain why smaller pieces of salt dissolve faster than
larger ones? You may use an illustration or diagram in your explanation.
The Effect of Temperature
Activity 5 will let you investigate how well coffee or powdered juice
dissolves in cold and in hot water.
Activity 5
How Well Does Coffee or Powdered Juice Dissolve in
Hot Water? In Cold Water?
1. Discuss how your group mates how you will do your investigation. Write
your hypothesis in a testable form. Describe a test you could conduct to
find out how well coffee or powdered juice dissolves in cold and in hot
water.
2. Identify variables (for example, amount of amount of coffee or powdered
juice) that you need to control in order to have a fair test.
3. Identify the dependent and independent variables.
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Diversity of Materials in the Environment
4. List all the materials you need, including the amount and ask these from
your teacher.
5. Do your investigation using the proper measuring devices. Be sure to
record your observations and tabulate them. Write everything you
observed during the dissolving test. These observations are the evidence
from which you can draw your conclusions.
6. Identify variables (for example, amount of amount of coffee or powdered
juice) that you need to control in order to have a fair test.
7. Identify the dependent and independent variables.
8. List all the materials you need, including the amount and ask these from your teacher.
9. Do your investigation using the proper measuring devices. Be sure to
record your observations and tabulate them. Write everything you
observed during the dissolving test. These observations are the evidence from which you can draw your conclusions.
10. What is your conclusion? Does coffee dissolve well in cold or in hot
water? Does powdered juice dissolve well in cold or in hot water? Use
the observations and results you recorded to explain your answer. 11. Does your conclusion support or reject your hypothesis? Explain your
results.
12. What is your conclusion? Does coffee dissolve well in cold or in hot water? Does powdered juice dissolve well in cold or in hot water? Use the observations and results you recorded to explain your answer.
13. Does your conclusion support or reject your hypothesis? Explain your
results.
Grade 7 Science: Matter 16
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The Nature of Solute
In Activity 6, you will find out if: (1) sugar dissolves better in hot than in
cold water, and (2) salt dissolves better in hot than in cold water.
Activity 6
Which Dissolves Faster in Hot and in Cold Water:
Sugar or Salt?
1. Discuss with your group mates how you will do your investigation.
2. Write your hypothesis in a testable form. Describe a test you could
conduct to find out answers to the given two questions above.
3. Identify variables (for example, amount of amount of coffee or powdered
juice) that you need to control in order to have a fair test.
4. Identify the dependent and independent variables.
5. List all the materials you need, including the amount and ask these from
your teacher.
6. Do your investigation using the proper measuring devices. Be sure to record your observations and tabulate them. Write everything you
observed during the dissolving test. These observations are the evidence from which you can draw your conclusions.
7. What is your conclusion? Does coffee dissolve well in cold or in hot water? Does powdered juice dissolve well in cold or in hot water? Use the observations and results you recorded to explain your answer.
8. Does your conclusion support or reject your hypothesis? Explain your
results.
The following questions can guide you:
a. Does sugar dissolve better in hot water than in cold water? Explain your answer, based on your observations from the investigation.
b. Does salt dissolve better in hot than in cold water? Explain your
answer, based on your observations from the investigation.
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c. Which is affected most by increasing the temperature of the water—the solubility of salt or the solubility of sugar? Explain
your answer.
You learned from Activity 5 that in general, a solute easily dissolves in
water when you increase the temperature. But the effect of temperature is
not that simple. The type or nature of the solute will affect its solubility.
You observed from Activity 6 that increasing the temperature either
makes a solid more soluble or less soluble in water. For some solutes,
increasing the temperature does not have any effect on the solubility of the
solute.
Now that you have completed the activities in this module, you have
learned the properties of a solution, the ways of reporting its concentration,
as well as the effects of stirring, particle size, temperature, and type of
solute on how fast a solid dissolves in water.
While learning about solutions, you also had the chance to gather
information and gain new knowledge through the process of conducting
science investigations. You also learned the importance of identifying the
variables that had to be controlled in order to make a good plan for
measuring and testing the variables you are concerned about.
What you have started doing in these investigations is what scientists
usually do when they seek answers to a scientific question or problem. In
the next modules, you will be challenged to ask more questions about
materials around you. You will try to explain answers to your hypothesis
(your suggested explanation) after you have done your investigation.
Grade 7 Science: Matter 18
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References and Links
Brady, J.E. & Senese, F. (2004). Chemistry: Matter and its changes, 4th
edition. River Street Hoboken, NJ: John Wiley & Sons, Inc.
Bucat, R.B. (Ed.) (1984). Elements of chemistry: Earth, air, fire & water,
Volume 2. Canberra City, A.C.T., Australia.
Elvins, C., Jones, D., Lukins, N., Miskin, J., Ross, B., & Sanders, R. (1990).
Chemistry one: Materials, chemistry in everyday life. Port Melbourne,
Australia: Heinemann Educational Australia.
Hill, J.W. & Kolb, D.K. (1998). Chemistry for changing times, 8th
edition.Upper Saddle River, NJ: Prentice Hall.
Kurtus, Ron (13 January 2006). Mixtures. Retrieved Jan 9, 2012 from http://www.school-for-champions.com/chemistry/mixtures.htm
Philippines. Department of Education. (2004).Chemistry: Science and
technology textbook for 3rd year. (Revised ed.). Quezon City: Author.